The invention relates to electronic devices, and, more particularly, to semiconductor capacitors and methods of fabrication.
Increasing demand for semiconductor memory and competitive pressures require higher density integrated circuit dynamic random access memories (DRAMs) based on one-transistor plus one-capcitor memory cells. But down scaling capacitors with the standard silicon oxide and nitride dielectric presents problems including decreasing quantity of charge stored in a cell. Consequently, alternative dielectrics with dielectric constants greater than those of silicon oxide and nitride are being investigated. Various dielectric materials are available; such as tantalum pentoxide (dielectric constant about 25 versus silicon nitride""s dielectric constant of about 7) as described in Ohji et al, Ta2O5 capacitors"" dielectric material for Giga-bit DRAMs, IEEE IEDM Tech. Dig. 5.1.1 (1995); lead zirconate titanate (PZT) which is a ferroelectric and supports nonvolatile charge storage (dielectric constant xcx9c1000) described in Nakamura et al, Preparation of Pb(Zr,Ti)O3 thin films on electrodes including IrO2, 65 Appl.Phys.Lett. 1522 (1994); strontium bismuth tantalate (also a ferroelectric) described in Jiang et al, A New Electrode Technology for High-Density Nonvolatile Ferroelectric (SrBi2Ta2O9) Memories, VLSI Tech. Symp. 26 (1996); and barium strontium titanate (dielectric constant about 500) described in Yamamichi et al, An ECR MOCVD (Ba,Sr)TiO3 based stacked capacitor technology with RuO2/Ru/TiN/TiSix storage nodes for Gbit-scale DRAMs, IEEE IEDM Tech. Dig. 5.3.1 (1995), Yuuki et al, Novel Stacked Capacitor Technology for 1 Gbit DRAMs with CVD-(Ba,Sr)TiO3 Thin Films on a Thick Storage Node of Ru, IEEE IEDM Tech.Dig. 5.2.1 (1995), Oh et al, A Stack Capacitor Technology with (Ba,Sr)TiO3 Dielectrics and Pt Electrodes for 1 Giga-Bit density DRAM, VLSI Tech. Symp. 24 (1996). Also see Dietz et al, Electrode influence on the charge transport through SrTiO3 thin films, 78 J.Appl.Phys. 6113 (1995) describes electrodes of Pt, Pd, Au, . . . on strontium titanate); US Patent No. 5,003,428 (PZT and barium titanate), U.S. Pat. No. 5,418,388 (BST, SrTiO3, PZT, PLZT, . . . ), and U.S. Pat. No. 5,566,045 (thin Pton BST).
However, each of these dielectric or ferroelectric materials and capacitor structures has problems such as adhesion to commonly used silicon integrated circuit materials (e.g., silicon dioxide), oxygen diffusion, and leakage currents.
The present invention provides contact materials for barium strontium titanate which give a Schottky barrier height greater than that of comparable (epitaxial or polycrystalline) platinum contacts and also provides oxygen compensating adhesion materials for very thin contacts.
The invention has advantages including low leakage currents and limited dielectric degradation.